The interaction of Eu(9-ANCA)(3) (9-ANCA = anthracene-9-carboxylic acid) with DNA has been investigated by a fluorescence method. Potentiometric equilibrium measurements have been performed at (25.0 +/- 0.1)degrees C and ionic strength 1 = 0.1 mol.dm(-3) KNO(3) for the interaction of Eu(III) and 9-ANCA with adenosine 5'-diphosphate (ADP), adenosine 5'-triphosphate (ATP), N-acetyl glutamic acid (Nc-Glu), N-acetyl leucine (Nc-Leu), and N-acetyl lysine (Nc-Lys) in a 1:1:1 ratio. The formation of various mixed ligand complexes was inferred from the potentiometric titration curves. The formation constants of the binary and ternary complexes have been refined with the SUPERQUAD computer program. The interaction of Eu(III)-(9-ANCA) with Nc-Glu, Nc-Leu, and Nc-Lys has been investigated by electroanalytical methods including cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon (GC) electrode.